Hack support for terrible RSA key-lengths in cryptography 43.0 (#4290)
diff --git a/scapy/layers/tls/cert.py b/scapy/layers/tls/cert.py
index ed934e8..24f1a6a 100644
--- a/scapy/layers/tls/cert.py
+++ b/scapy/layers/tls/cert.py
@@ -44,12 +44,27 @@
from scapy.layers.tls.crypto.pkcs1 import pkcs_os2ip, _get_hash, \
_EncryptAndVerifyRSA, _DecryptAndSignRSA
from scapy.compat import raw, bytes_encode
+
if conf.crypto_valid:
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa, ec
+ # cryptography raised the minimum RSA key length to 1024 in 43.0+
+ # https://github.com/pyca/cryptography/pull/10278
+ # but we need still 512 for EXPORT40 ciphers (yes EXPORT is terrible)
+ # https://datatracker.ietf.org/doc/html/rfc2246#autoid-66
+ # The following detects the change and hacks around it using the backend
+
+ try:
+ rsa.generate_private_key(public_exponent=65537, key_size=512)
+ _RSA_512_SUPPORTED = True
+ except ValueError:
+ # cryptography > 43.0
+ _RSA_512_SUPPORTED = False
+ from cryptography.hazmat.primitives.asymmetric.rsa import rust_openssl
+
# Maximum allowed size in bytes for a certificate file, to avoid
# loading huge file when importing a cert
@@ -263,9 +278,18 @@
pubExp = pubExp or 65537
if not modulus:
real_modulusLen = modulusLen or 2048
- private_key = rsa.generate_private_key(public_exponent=pubExp,
- key_size=real_modulusLen,
- backend=default_backend())
+ if real_modulusLen < 1024 and not _RSA_512_SUPPORTED:
+ # cryptography > 43.0 compatibility
+ private_key = rust_openssl.rsa.generate_private_key(
+ public_exponent=pubExp,
+ key_size=real_modulusLen,
+ )
+ else:
+ private_key = rsa.generate_private_key(
+ public_exponent=pubExp,
+ key_size=real_modulusLen,
+ backend=default_backend(),
+ )
self.pubkey = private_key.public_key()
else:
real_modulusLen = len(binrepr(modulus))
@@ -470,9 +494,18 @@
# in order to call RSAPrivateNumbers(...)
# if one of these is missing, we generate a whole new key
real_modulusLen = modulusLen or 2048
- self.key = rsa.generate_private_key(public_exponent=pubExp,
- key_size=real_modulusLen,
- backend=default_backend())
+ if real_modulusLen < 1024 and not _RSA_512_SUPPORTED:
+ # cryptography > 43.0 compatibility
+ self.key = rust_openssl.rsa.generate_private_key(
+ public_exponent=pubExp,
+ key_size=real_modulusLen,
+ )
+ else:
+ self.key = rsa.generate_private_key(
+ public_exponent=pubExp,
+ key_size=real_modulusLen,
+ backend=default_backend(),
+ )
self.pubkey = self.key.public_key()
else:
real_modulusLen = len(binrepr(modulus))
